Received-SPF: pass (google.com: domain of linux-kernel-owner@vger.kernel.org designates 2620:137:e000::1:20 as permitted sender) client-ip=2620:137:e000::1:20;
Message-ID: <ca5090c2-35d6-c507-7fb2-c293712cd53f@linaro.org>
Date:   Sat, 24 Sep 2022 19:46:33 +0200
MIME-Version: 1.0
User-Agent: Mozilla/5.0 (X11; Linux x86_64; rv:91.0) Gecko/20100101
 Thunderbird/91.11.0
Subject: Re: [PATCH v4 01/30] thermal/core: Add a generic
 thermal_zone_get_trip() function
Content-Language: en-US
To:     Marek Szyprowski <m.szyprowski@samsung.com>, rafael@kernel.org
Cc:     linux-kernel@vger.kernel.org, linux-pm@vger.kernel.org,
        rui.zhang@intel.com, Amit Kucheria <amitk@kernel.org>
References: <20220921094244.606948-1-daniel.lezcano@linaro.org>
 <20220921094244.606948-2-daniel.lezcano@linaro.org>
 <CGME20220923221936eucas1p1e01148605c9aaf27d8d71969feb99144@eucas1p1.samsung.com>
 <c85a77a3-409b-3e83-08a7-ac7e1888790d@samsung.com>
From:   Daniel Lezcano <daniel.lezcano@linaro.org>
In-Reply-To: <c85a77a3-409b-3e83-08a7-ac7e1888790d@samsung.com>
Content-Type: text/plain; charset=UTF-8; format=flowed
Content-Transfer-Encoding: 8bit
Precedence: bulk

On 24/09/2022 00:19, Marek Szyprowski wrote:
> Hi Daniel,
> 
> On 21.09.2022 11:42, Daniel Lezcano wrote:
>> The thermal_zone_device_ops structure defines a set of ops family,
>> get_trip_temp(), get_trip_hyst(), get_trip_type(). Each of them is
>> returning a property of a trip point.
>>
>> The result is the code is calling the ops everywhere to get a trip
>> point which is supposed to be defined in the backend driver. It is a
>> non-sense as a thermal trip can be generic and used by the backend
>> driver to declare its trip points.
>>
>> Part of the thermal framework has been changed and all the OF thermal
>> drivers are using the same definition for the trip point and use a
>> thermal zone registration variant to pass those trip points which are
>> part of the thermal zone device structure.
>>
>> Consequently, we can use a generic function to get the trip points
>> when they are stored in the thermal zone device structure.
>>
>> This approach can be generalized to all the drivers and we can get rid
>> of the ops->get_trip_*. That will result to a much more simpler code
>> and make possible to rework how the thermal trip are handled in the
>> thermal core framework as discussed previously.
>>
>> This change adds a function thermal_zone_get_trip() where we get the
>> thermal trip point structure which contains all the properties (type,
>> temp, hyst) instead of doing multiple calls to ops->get_trip_*.
>>
>> That opens the door for trip point extension with more attributes. For
>> instance, replacing the trip points disabled bitmask with a 'disabled'
>> field in the structure.
>>
>> Here we replace all the calls to ops->get_trip_* in the thermal core
>> code with a call to the thermal_zone_get_trip() function.
>>
>> While at it, add the thermal_zone_get_num_trips() to encapsulate the
>> code more and reduce the grip with the thermal framework internals.
>>
>> Signed-off-by: Daniel Lezcano <daniel.lezcano@linaro.org>
> 
> This patch landed in linux next-20220923 as commit 78ffa3e58d93
> ("thermal/core: Add a generic thermal_zone_get_trip() function").
> Unfortunately it introduces a deadlock:
> 
> thermal_zone_device_update() calls handle_thermal_trip() under the
> tz->lock, which in turn calls thermal_zone_get_trip(), which gathers
> again tz->lock. I've tried to fix this by switching
> handle_thermal_trip() to call __thermal_zone_get_trip().
> 
> This helps for fixing the issue in this change, but then I've tried to
> apply it on top of linux next-20220923. Unfortunately it fails again. It
> looks that the other changes also assumes that calling
> thermal_zone_get_trip() is possible under the tz->lock, because in my
> case it turned out that handle_non_critical_trips() called
> step_wise_throttle(), which in turn called thermal_zone_get_trip(). I
> gave up fixing this. Please re-check possible call paths and adjust
> locking to them.

Yes, you are correct. Those paths have the lock held. I'm fixing this


-- 
<http://www.linaro.org/> Linaro.org │ Open source software for ARM SoCs

Follow Linaro:  <http://www.facebook.com/pages/Linaro> Facebook |
<http://twitter.com/#!/linaroorg> Twitter |
<http://www.linaro.org/linaro-blog/> Blog